Post-Translational Mechanisms of Plant Circadian Regulation

Abstract

The molecular components of the circadian system possess the interesting feature of acting together to create a self-sustaining oscillator, while at the same time acting individually, and in complexes, to confer phase-specific circadian control over a wide range of physiological and developmental outputs. This means that many circadian oscillator proteins are simultaneously also part of the circadian output pathway. Most studies have focused on transcriptional control of circadian rhythms, but work in plants and metazoans has shown the importance of post-transcriptional and post-translational processes within the circadian system. Here we highlight recent work describing post-translational mechanisms that impact both the function of the oscillator and the clock-controlled outputs.

Role of Circadian Rhythms in Major Plant Metabolic and Signaling Pathways

“…This endogenous oscillator is generally comprised of three different modules: (i) input pathway, which gives information about the surrounding environment; (ii) central oscillator that consists of “canonical clock gene,” which composes the elite clock design; and (iii) the output pathway that constitutes the clock-driven downstream processes. The central oscillator includes complex TTFLs ( de Dios et al, 2018 ) that blend with the post-transcriptional and post-translational modifications ( Dalchau et al, 2011 ; Yan et al, 2021 ). The circadian clock has a self-reliant mechanism and their metabolic processes can also be administered by circadian rhythm, which was previously studied with the model plant Arabidopsis , also in the potato, and rice crops ( Kim et al, 2017 ; Inoue et al, 2018 ).…”

Genome-Wide Identification and Characterization of PRR Gene Family and their Diurnal Rhythmic Expression Profile in Maize

“…The circadian clock is an autonomous oscillator that produces endogenous biological rhythms of a period of about 24 h and plays crucial roles in coordinating the development and metabolism with daily and seasonal changes through the synchronous expression of genes involved in related biological processes. Many clock-associated genes constitute an interlocked transcription and translation feedback loops to maintain the function of the circadian clock, in which clock-associated genes regulate each other to generate oscillations with expression peaks at specific times during the daily cycle [ 1 – 5 ]. Pseudo-response regulators are important components of the core of circadian clock.…”

“…Each member contains a pseudo-receiver (PR) domain of approximately 120 amino acids at its N-terminus and a CCT motif of approximately 50 amino acids at the C-terminal end [ 10 – 12 ]. The PR domain of PRRs allows oligomerization between the PRRs and bridges interactions of the PRRs and other proteins [ 5 , 7 , 11 , 13 – 15 ]. The transcriptional repression activity of PRRs relies on the presence of a functional CCT domain to recognize the target genes [ 7 , 16 – 18 ].…”

Arabidopsis thaliana PRR7 Provides Circadian Input to the CCA1 Promoter in Shoots but not Roots

“…In Arabidopsis thaliana , the core circadian oscillator includes multiple interlocking feedback loops of gene expression, modulated by post-translational control at several levels ( Harmer, 2009 ; Nohales and Kay, 2016 ; McClung, 2019 ; Sanchez et al, 2020 ; Yan et al, 2021 ). The first loop to be discovered comprised the morning-expressed MYB transcription factors CIRCADIAN CLOCK ASSOCIATED 1 (CCA1) and LATE ELONGATED HYPOCOTYL (LHY) and the evening-phased transcriptional repressor PSEUDO-RESPONSE REGULATOR 1 (PRR1, also known as TIMING OF CAB EXPRESSION 1, TOC1).…”